In many devices, wherein a substantial amount of heat is generated, there is a need for an active thermal control, in order to maintain the desired operational temperature for the device. A common solution is to use the air in the atmosphere for transport of the excessive heat by use of electromechanical fans or ventilators. This is an effective but sometimes noisy solution, wherefore conduction of the heat through passive or active heat conductors to a thermal radiator in many times is a preferred solution. In particular, in space applications, operating in vacuum, this is the only solution if direct radiation of the heat into space is impossible.
For example, in the development of small but very efficient spacecraft with high internal power density thermal control becomes a growing area of concern. The low thermal mass of a small spacecraft makes it necessary to radiate excessive heat when active, but on the other hand the internal part of the spacecraft must be thermally isolated from external radiator surfaces when passive in order to keep the internal temperature at an acceptable level. If the active and passive modes are synchronized with entering or leaving eclipse (earth shadow) the problem becomes even worse. To solve the problem an active thermal control system with a heat flux modulation capability must be used.
Such a heat flux modulation can be based on a number of design principles. A liquid can be pumped around in the system carrying the heat from the source to the radiator. Passive heat pipes (extremely good thermal conductors) or active heat pipes, in which a liquid in vapor phase is used in a tube to transport the heat. The heat transport capability in such a heat-pipe is normally directly related to the temperature on the hot side. In some variable active heat pipers, the heat transport capability can be controlled by controlling the boil rate of the liquid. Another alternative is mechanical systems, where mechanical switches are used together with very good thermal conductors, i.e. passive heat pipes. The mechanical switch creates a gap with very low thermal conductivity in the off-mode.
The heat flux modulation is a key parameter for all thermal control systems. Particular on the small spacecraft with a modern distributed functionality the mechanical system is most likely to prefer due to the simplicity, given that the heat switches have high modulation capability, are compact and have low mass.
A switch designed for high thermal conductivity may naturally be particularly useful as an electrical conductor as well. When optimized for high electrical conductivity such a switch may be used as a high current electrical switch.
However, in general, mechanical switches according to prior art have rather low heat flux modulation capability or current switching capability, especially in relation to their physical size. In particular, since the trend is that other components of spacecraft or other systems are miniaturized using for example Microsystems Technology (MST) or Microelectromechanical Systems (MEMS), conventional mechanical switches become too large and inefficient, or cannot readily be implemented in such a miniaturized system.